X-ray tube having a mica window



Jan. 5, 1954 J BLEEKSMA 2,665,391

X-RAY TUBE HAVING A MICA WINDOW Filed March 4, 1950 5 7 7 A k s I 10 1," J @MNBLEJEES'A/M INVENTOR.

AGENI.

Patented Jan. 5, 1954 2,665,391 X-RAY TUBE HAViNG A MICA WINDOW Jan Bleeksma, Mount Vernon, N. Y., assignor to Amperex Electronic Corporation, Brooklyn,

Application March 4, 1950, Serial No. 147,739

My invention relates to X-ray tubes and particularly to X-ray tubes for X-ray difiraction purposes.

In general for X-ray diffraction study, it is desirable to have a tube with a relatively large output of X-radiation. In the prior art such tubes have been provided with windows which permitted afair output of X-radiation but which had several disadvantages. Such windows either were difficult to fabricate, and assemble into the tube structure, or they resulted in considerable leakage.

It is an object of my invention to provide an X-ray tube for X-ray diffraction study which is superior to and has striking advantages over existing X-ray tubes.

It is a further object of my invention to provide a window for an X-ray tube having a relatively large output of X-radiation which is relatively easy to fabricate and assemble into the tube structure and which is secure against undesired leakage.

It is a still further object of my invention to provide a window construction for an X-ray tube in which the window is protected from undesired electronic bombardment as a result Of secondary emission from the anode target.

These and further objects of my invention will appear as the specification progresses.

According to the invention, an X-ray tube, primarily for X-ray difiraction study, is provided with a radiation permeable window which comprises a thin disc of insulating material which is permeable to X-radiation and which is sealed to the tube envelope in a vacuum-tight fashion and a thin foil of conductive material interposed between the disc of insulating material and the target of the tube to protect the latter from electron bombardment by providing a conductive path for electrons striking the window.

In the preferred embodiment of my invention, a thin mica disc is powder-glass sealed in a window support sealed to the walls of the tube envelope thereby providing a vacuum-tight window for the tube. Between the mica window and the target and supported by the walls of the tube envelope is a thin disc of beryllium which protects the mica window from electron bombardment.

The invention, however, is not restricted to this particular combination since I have found that aluminum, although somewhat less desirable, is suitable in place of beryllium, and of course the mica window could be replaced with other types 5 Claims. (Cl. 313-59) 2 of windows having a relatively low absorption for X-rays.

The invention will be described with reference to the drawing in which Fig. 1 shows a conventional X-ray tube for X-ray diffraction study provided with a window according to the invention and Fig. 2 shows the window construction in greater detail.

Fig. 1 shows an Xray tube for diffraction purposes provided with a sealed and evacuated envelope I, a cathode 2, and an anode 3. The envelope at the level of the target is provided with four windows 4 of the type about to be described, through which a beam of X-radiation emerges. Provision is made in the jacket 5 for supplying power to energize the tube.

The window construction is shown in greater detail in Fig. 2. The window comprises a ringshaped support 6 of stainless steel which is sealed to the envelope with powder-glass l. Seated on a ridge in the support is a mica disc 8 having athickness of about 0.0003 to 0.0005 inch, which is sealed to the support with powder-glass 9 thereby providing a vacuum-tight seal for the window. Seated beneath the support and supported by the envelope is a disc of beryllium l8- having a thickness of about 0.004 to 0.006 inch, which is sealed in place but is not vacuum-tight, and which serves to protect the mica disc from electron bombardment.

The absorption of X-rays by the mica and beryllium discs has been found to be about the same or less than absorption of X-rays by vacuum-tight beryllium discs which must be thicker to prevent atmospheric penetration of the beryllium, thereby destroying the vacuum in the tube.

While I have disclosed my invention with specific examples and applications thereof, other obvious variants will be apparent to those skilled in the art Without departing from the spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. An X-ray tube comprising an evacuated envelope, cathode and anode electrodes, and a radiation permeable window in a wall portion of said envelope facing said anode, said window comprising a metallic window support powder-glass sealed into said envelope, a mica window seated in said support and powder-glass sealed thereto to provide a vacuum-tight seal for said mica disc, and a thin foil of radiation permeable metal secured to said envelope between said support and the anode of the tube to provide a conductive path for electrons striking the window.

2. An X-ray tube comprising an evacuated envelope, cathode and anode electrodes facing said anode, and a radiation permeable window in a wall portion of said envelope, said window comprising a window support powder-glass sealed into said envelope, a mica window seated in said support and powder-glass sealed thereto to provide a vacuum-tight seal for the mica disc, and a thin foil of beryllium interposed between the mica window and the anode of the tube to provide a conductive path for electrons striking thewindow. H l h 3. An X-ray tube comprising an evacuated envelope, cathode and anode electrodes, and a radiation permeable window in a wall portion of said envelope facing said anode, said window comprising a mica disc vacuum sealed to said envelope, and a thin beryllium disc interposed between the mica disc and the anode of the tube to provide a conductive path for electrons striking the window.

4. An X-ray tube comprising an evacuated envelope, cathode and anode electrodes, and a radiation permeable window in a wall portion of said envelope facing said anode, said window comprising a metallic window support powderglass sealed to said envelope, a mica window seated in said support and powder-glass sealed thereto to provide a vacuum-tight seal for the mica window, and a beryllium window secured to the walls of the envelope and interposed between the mica window and the anode of the tube for providing a conductive path for elec trons striking the window.

5. An X-ray tube comprising an evacuated References Cited in the file of this patent UNITED STATES PATENTS Number Name Date. 1,626,465 Holst et al. Apr. 26, 1927 1,626,693 Rentschler May 3, 1927 1,927,475 Volkel Sept. 19, 1933 2,009,457 Sloan July 30, 1935 2,024,332 Bouwers Dec. 17, 1935 2,125,700 Volkel Aug., 2, 1938 2,356,645 .Atlee et al. Aug. 22, 1944 

